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Get your credit report from annualcreditreport.com , and look at any derogatory (bad) items. Those need to be paid off in full, or corrected if there is an error. After that, it's just a waiting game, while you keep paying all your bills in full.

If you cannot pay your bills in full, maybe see a credit counselor, who can suggest changes in your lifestyle so that you can.

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Pay all your bills on time. If you don't have an open, active loan or credit card, get a credit card even if you have to get a secured card. Use the card for regular purchases and pay the statement balance in full every month.

You need at least 24 months of consistent, on time payment history to improve your score. There are no shortcuts. It's just a matter of on time payment history.